Defender of the faith: Benedict XVI, seen here on Ash Wednesday, proved that the Catholic restoration was not the aberration of a Polish pope

There was perhaps an intimation of Pope Benedict XVI's intention to resign as pope when on January 6 Monsignor Georg Gänswein, for a decade his private secretary, was ordained a bishop with the title Archbishop of Urbs Salvia and appointed Prefect of the Papal Household. Only those in Pope Benedict's inner circle can be sure of its human dynamics, but from all appearances, Monsignor Gänswein was an indispensable aide to the ageing pontiff. If he was to move on, then no doubt Pope Benedict meant to move on too.

There have been only three cases in the 2,000-year history of the Catholic Church of a papal resignation or abdication and none that exactly matches this one. On all previous occasions, outside powers came into play — the Emperor Henry III in the case of Gregory IX, the German King Sigismund in the case of Gregory XII, and between the two, in 1294, there was Celestine V who became the puppet of Charles II of Naples and Sicily. Today, not even the most extreme conspiracy theorists could believe that President Obama or Chancellor Merkel had any hand in Pope Benedict's decision. If he were looking for a precedent, Celestine V was the most comparable: Pietro del Morrone was a hermit, elected at the age of 85, who quickly realised he was not up to the job. He consulted Cardinal Caetani, the Vatican's leading canon lawyer, as to whether it was possible for him to resign. Caetani ruled that it was. Celestine was duly stripped of his papal insignia and Caetani elected pope (Boniface VIII) in his stead.

Celestine V was pope for less than a year: Benedict XVI has held the office for almost eight years. Unlike Celestine, his many years as Prefect for the Congregation for the Doctrine of the Faith (CDF)made him familiar with the workings of papal government and as pope he was able to enact a number of controversial measures. His motu proprio authorising any priest to celebrate the Latin Tridentine mass was opposed by many bishops who had hitherto sought to restrict it. It was courageous and imaginative to found the Ordinate of Our Lady of Walsingham, a prelature that would enable Anglicans to come into communion with the Catholic Church while retaining much of their liturgy and practice. His removal of all obstacles to a reconciliation with the Society of Pius X (SSPX), the followers of the late Archbishop Lefebvre, was also controversial and much misunderstood: it was erroneously taken to condone or pass over the denial of the Holocaust by one of the SSPX bishops, Bishop Richard Williamson — a grotesque distortion of which the pope was undoubtedly unaware.

In his seven years in office, Pope Benedict has also demonstrated his intellectual vigour by writing some outstanding Encyclicals. The first, Deus Caritas Est, encouraged some liberal Catholics to believe that the Pope had come to terms with the permissive society. It seemed to rehabilitate Eros. "Love between man and woman, where body and soul are inseparably joined," he wrote "would seem to be the very epitome of love." One parish priest in West London claimed from the pulpit that the Encyclical provided a theological framework for civil partnerships (same-sex marriage had not yet appeared on the horizon).

Pope Benedict's Apostolic Exhortation, Sacramentum Caritatis, published in March 2007, dashed these hopes: it demonstrated beyond doubt that the leopard had not changed its spots. In part a summary of the Synod of Catholic Bishops held in Rome in 2005, it was a lucid exposition of the Church's teaching on the Eucharist, and a reminder of its place at the very heart of Catholic belief. The priest's words of consecration at the Mass, wrote Pope Benedict, effect "a sort of ‘nuclear fission', to use an image familiar to us today, which penetrates to the heart of all being, a change meant to set off a process which transforms reality, a process leading ultimately to the transfiguration of the entire world."